The second type of duos that look together are those who each have three lines and share two of them. I have provided an equation below.

ABC + ABD​

The key elements are this 1. both individuals have three lines; 2. the duo shares two lines.

When these elements are combined it creates a duo pleasing to the eye who, while not bringing out so many of each other's features, often bring about the feeling that they are individuals cut from the same cloth - no matter how different they may otherwise be.